I always smile for photos. My alien registration card had the same picture as my passport, same with my school ID.... ack, I just double checked, no smile at all and my eye is twitching in the photo

If you are smiling and laughing to yourself on a train, then whoever you are facing might feel self conscious (no matter what country you are in). If you are really loud on a train talking in English, with or without giggling or laughing, someone is bound to get pissed off. Many are self conscious when you talk in English because they don't understand what you are talking about.

When I am walking by people though, most of them do not make eye contact or even acknowledge my existance. It doesn't bother me though otherwise I might be embarrassed for staring at them the entire time

I am sure foreigners in New York would say the same thing about Americans ignoring them on the streets. Too many people to give a damn.